Facebook's (FB) Sponsored Stories mobile news feed ads have a click rate nearly twice that for its PC news feed ads, and 13.7x as high as that for its PC ads in general, according to TBG Digital. Moreover, the revenue rate for 1,000 mobile ads is 165% higher than that for PC news feed ads. That has to sit well with investors worried about Facebook's ability to monetize mobile viewing. One caveat: Facebook only recently began selling mobile ads, thus TBG's sample size is limited. (yesterday)